linux-kernel - Re: [PATCH v3 1/2] IMA: Define workqueue for early boot "key" measurements

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Message-ID: <c60341a3-2329-cd92-c76c-6f8249a57b43@linux.microsoft.com>
Date:   Thu, 12 Dec 2019 18:59:39 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>, linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthewgarrett@...gle.com,
        sashal@...nel.org, jamorris@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org
Subject: Re: [PATCH v3 1/2] IMA: Define workqueue for early boot "key"
 measurements

On 12/12/2019 6:32 PM, Mimi Zohar wrote:

>>>
>>> Don't you need a test here, before setting ima_process_keys?
>>>
>>> 	if (ima_process_keys)
>>> 		return;
>>>
>>> Mimi
>>
>> That check is done before the comment - at the start of
>> ima_process_queued_keys().
> 
> The first test prevents taking the mutex unnecessarily.
> 
> Mimi

I am trying to understand your concern here. Could you please clarify?

  => If ima_process_keys is false
       -> With the mutex held, should check ima_process_keys again 
before setting?

Let's say 2 or more threads are racing in calling ima_process_queued_keys():

The 1st one will set ima_process_keys and process queued keys.

The 2nd and subsequent ones - even if they have gone past the initial 
check, will find an empty list of keys (the list "ima_keys") when they 
take the mutex. So they'll not process any keys.

thanks,
  -lakshmi